Note 9 - Employee Benefit Program (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Oct. 31, 2020	Jan. 01, 2019
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount	$ 19,500	$ 18,500	$ 18,500
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	4.50%	4.50%	4.50%
Defined Contribution Plan, Cost	$ 513,000	$ 449,000	$ 470,000
BTC [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	4.50%	4.50%	4.50%
Defined Contribution Plan, Cost	$ 19,000	$ 19,000	$ 21,000
Defined Contribution Plan, Minimum Annual Contributions Per Employee, Percent					1.00%
Multiemployer Plan, Employer Contribution, Cost, Total	$ 0	$ 0	$ 0
RSP [Member]
Multiemployer Plan, Pension, Significant, Employer Contribution under Collective-Bargaining Arrangement to All Participating Employer Contributions, Percentage	0.30%
Multiemployer Plan, Pension, Significant, Employees Covered by Collective-Bargaining Arrangement to All Participants, Percentage	0.10%
Defined Benefit Plan, Funded Percentage					100.10%
Multiemployer Plan, Pension, Significant, Plan Asset				$ 2,100,000,000